This invention relates to a process for depositing a titanium nitride film which is widely used in LSI production as a barrier metal layer in a contact hole and an embedded plug, for improving migration resistance of a multilayered aluminum interconnection, and as a film for an anti-reflection coating.
In the production of LSIs, aluminum and tungsten are employed in metal interconnection for an interlayer electric contact through contact holes and via holes. Direct contact of the aluminum or the tungsten with the silicon wafer, however, may induce alloying or silicidation of the metal and intrusion of the resulting electroconductive substance into the silicon wafer to result in a significant increase of leakage current. Use of aluminum for the interconnection may also induce the problem of shortened life of the interconnection through stress migration and electromigration. Furthermore, since aluminum has a high UV reflectance, UV light projected onto the aluminum interconnection by a stepper is reflected on the aluminum surface to diffuse into the resist film and induce pattern defects, and in turn, a decrease in resolution. To prevent such problems, there has been proposed a deposition of a titanium nitride film over or underneath the metal interconnection to form a bi-layered or a sandwich-like tri-layered structure. The titanium nitride film has effectively suppressed metal diffusion to prevent the alloying and silicidation as well as the migration. Deposition of the titanium nitride film has also reduced the UV reflection on the aluminum surface to thereby prevent the resolution decrease. Furthermore, titanium nitride, which is highly electroconductive, would not reduce the conductance of the interconnection.
For producing a titanium nitride film, conventional processes such as deposition by reactive sputtering and nitrization of a metal titanium film have been widely used in the art. However, such conventional processes have proved ineffective under the recent pattern design rule of submicron order wherein steps on the surface have become steeper and the contact via holes have become deeper and narrower with an enlarged aspect ratio. More illustratively, the steps and the side wall of the holes could not be fully covered by physical vapor deposition techniques such as sputtering, and nowadays, chemical vapor deposition (CVD) techniques enabling higher step coverage are beginning to be used.
Japanese Patent Laid Open No. Sho. 60(1985)-245233 and Hei. 03(1991)-64473, for example, disclose an atmospheric pressure or a low pressure chemical vapor deposition of the titanium nitride film by using titanium (IV) chloride with nitrogen, hydrogen, or ammonia according to the following reactions (1) to (3). EQU 2TiCl.sub.4 +N.sub.2 =2TiN+4Cl.sub.2 ( 1) EQU 2TiCl.sub.4 +N.sub.2 +4H.sub.2 =2TiN+8HCl (2) EQU 2TiCl.sub.4 +2NH.sub.3 +H.sub.2 =2TiN++8HCl (3)
The reaction of the formula (1) requires a temperature as high as 1000.degree. C. or even higher, and the reactions of the formulae (2) and (3) requires a temperature of 500.degree. C. or higher.
A film deposition at such a high temperature is accompanied with the risk of deteriorated film properties due to diffusion of the doping layer of the semiconductor. Furthermore, the film deposition at such a high temperature exceeding the melting point of the aluminum could not be effected after the deposition and the patterning of the aluminum. Therefore, there is a strong demand for developing a CVD process which could be carried out at a temperature of up to 400.degree. C.
Japanese Patent Publication No. Sho. 57(1982)-42970 and Japanese Patent Laid Open No. Hei. 03(1991)-39474 disclose use of organic titanium compounds to deposit a titanium nitride film by chemical vapor deposition at a temperature of up to 400.degree. C. The organic titanium compounds disclosed therein such as tetrakis(trimethylamino)titanium and titanium dicyclopentadienyldiazide, however, are unstable and have a low vapor pressure, and therefore, use of such gas sources for the chemical vapor deposition have been unpractical for their insufficient film deposition rate.
In view of the above-described situation, an object of the present invention is to provide a CVD process at atmospheric pressure or a low pressure which is capable of depositing a high quality titanium nitride film at a low temperature and at a high deposition rate.
The inventors of the present invention have made an intensive study to solve the above-described problems, and completed the present invention after finding out that some organic chemical compounds of particular chemical compositions, which are stable and which have a high vapor pressure, may be used as a gas source for the low-temperature chemical vapor deposition to form a titanium nitride film of a high quality at a high deposition rate.